Sensory and Motor Mechanisms Chapter 50 Campbell Biology – 9th Edition

You must know The location and function of several types of sensory receptors How skeletal muscles contract Cellular events that lead to muscle contraction

Sensory Receptors ____________________________: physical stimuli – pressure, touch, stretch, motion, sound ____________________________: detect heat/cold ____________________________: transmit solute conc. info – taste (gustatory), smell (olfactory) ____________________________ receptors: detect EM energy – light (photoreceptors), electricity, magnetism _____________ receptors: respond to excess heat, pressure, chemicals

Sensation = action potentials reach brain via sensory neurons _________________________: receptor detects a stimulus Sensation = action potentials reach brain via sensory neurons _________________________: information processed in brain

Retina Optic nerve To brain Cone Photoreceptors Rod Neurons Pigmented epithelium Bipolar cell Amacrine Horizontal Optic nerve fibers Ganglion Vision Compound eyes: several thousand ommatidia (light detectors) with its own lens; insects & crustaceans Vertebrates: Rods: sense ___________ Cones: ________________ vision Rhodopsin: light-absorbing ________________ that triggers signal transduction pathway that leads to sight

Muscles always contract Muscles work in antagonistic pairs to move parts of body Biceps contracts Human Triceps relaxes Forearm flexes extends Extensor muscle Flexor Grasshopper Tibia

Skeletal Muscle Structure Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Nuclei Muscle Myofibril Dark band Sarcomere Z line Light band I band TEM A band 0.5 µm M line Thick filaments (myosin) H zone Thin filaments (actin) Attached to bones by __________ Types of muscle: _____________ (internal organs) _____________ (heart) _____________ (striated) 1 long fiber = single muscle cell Each muscle fiber = bundle of myofibrils, composed of: _________: thin filaments _________: thick filaments

______________: basic contractile unit of the _____________ Sarcomere 0.5 µm Z H A Relaxed muscle fiber I Contracting muscle fiber Fully contracted muscle fiber Z lines – border I band – _______ actin filaments A band – _______ myosin filaments

(Note: Filaments do ________________) Muscle Contraction: Sarcomere 0.5 µm Z H A Relaxed muscle fiber I Contracting muscle fiber Fully contracted muscle fiber Sarcomere relaxed: actin & myosin _____________________ Contracting: Muscle fiber stimulated by ________ ________________ Length of sarcomere is reduced ___________ slides over __________ Fully contracted: actin & myosin completely overlap ________________________________: thick & thin filaments slide past each other to increase overlap (Note: Filaments do ________________)

Muscle fibers only contract when stimulated by a motor neuron Ca2+ released from sarcoplasmic reticulum Mitochondrion Motor neuron axon Synaptic terminal T tubule Sarcoplasmic Myofibril Plasma membrane of muscle fiber Sarcomere ______ is released from the sarcoplasmic reticulum

Synaptic terminal of _________ neuron releases ____________ Muscle fiber _________ ______ released Initiate _____________ of _____________ Ca2+ CYTOSOL SR PLASMA MEMBRANE T TUBULE Synaptic cleft Synaptic terminal of motor neuron ACh

Depolarization of muscle cell releases _________  binds to _________  _______________________ Myosin-binding sites blocked. Myosin-binding sites exposed. Tropomyosin Ca2+-binding sites Actin Troponin complex Myosin- binding site Ca2+

Hydrolysis of ATP by myosin  cross-bridge formed  thin filament pulled toward center of sarcomere Thin filaments Thick filament Thin filament Thick filament Myosin head (low-energy configuration) Cross-bridge binding site Myosin head (high- energy configuration) Actin Myosin head (low- Thin filament moves toward center of sacomere.

Speed of muscle contraction: Fast fibers – brief, rapid, powerful contractions Slow fibers – sustain long contractions (posture)

Problems ALS (Lou Gehrig’s disease): degeneration of motor neurons, muscle fibers atrophy Botulism: block release of acetylcholine, paralyzes muscles Myasthenia gravis: autoimmune disorder, produce antibodies to acetylcholine Calcium deficiency: muscle spasms and cramps Rigor mortis (after death): no ATP to break actin/myosin bonds; sustained muscle contraction until breakdown (decomposition)